Method of hardening photographic gelatin



Patented Jan. 7, 1941 UNITED STATES PATENT A OFFICE METHOD or nmnnmnc PHOTOGRAPHIC GELATIN Samuel E. Sheppard and Robert C. Houck, Rochester, N. Y assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application October 23, 1936, Serial No. 107,274

7 Claims. (0!. 95-7) This inventionrelate's to prehardened gelatin I for photographic emulsions and to a method for tions, particularly under tropical conditions.

Compounds which have been used for the purpose of hardening gelatin and emulsions include chrome alum, formaldehyde, and others. In our prior application, Seria1 No. 745,754, filed Septemher 27, 1934, we disclosed the use of hydroxy aldehydes up to and including pentoses for this pur- There are a number of objections to these hardening compounds when employed in the usual way. An excess of the hardening agent ordinarily remains in the gelatin and this excess hardening compound produces undesirable rsults in the gelatin and in the emulsions made from it. Among these objectionable characteristics are a proflressive rise in viscosity of the gelatin at the usual coating temperature so, that uncertainties and difliculties in the matter of coating control are introduced; a further objection is the bringing about of a progressive hardening over a period of time after the emulsion is coated and dried.

This latter feature is objectionable not only because of the uncertain condition of the material thereby produced unless a very long period of seasoning is resorted to. but also because of the pr ressive change in the photographic or sensitometric properties, such as the development rate. A further objectionable feature in the use of excess hardening agents, particularly aldehydes, is that the 'uncombined hardening agent tends to produce fog.

We have found that the undesirable features referred to above may be-attributed in a large measure to the excess or uncombined hardening agent in the gelatin or emulsion. We therefore propose to treat the gelatin in an aqueous bath of x a hardening agent for a definite length of time and then wash out the residual uncomblned hardening agent. 7

In carrying out our invention, a solution of gelatin is mixed with an aqueous solution of a hardening agent such as an aldehyde and permitted to stand for an appreciable length of time, for example, from 18 to '72 hours depending on concentration of aldehyde, pH, and temperature of storage. The gelatin, may also be immersed in the aldehyde hardening solution in the form of gelatin sheets or noodles. The excess-aldehyde or other hardening agent is then washed out of the gelatin with water and the gelatin is mixed with a silver halide emulsion or coated as a separate layer on a photographic support, or in the case of the sheets or noodles, may be dried and retained for future use. The gelatin treated in this way may have a melting point of from 40 C. to C. with a water content of about 10%.

Among the hardening agents which may be used for treating gelatin according to our invention are formaldehyde and other aldehydes, and the hydroxy aldehydes disclosed in our prior application, Serial No. 745,754. These are used in quantities up to 1% of the amount ofgelatin. The preferred pH of the hardening solution is 6 to 10.

The following method of procedure, which is by way of example only, illustrates a method of preparing ahardened gelatin having a substantially constant melting point according to our invention:

A 7% gelatin solution at pH 6.44 is treated with 0.3% of formaldehyde (based on the weight of the gelatin). The treated gelatin is allowed to gel and this gel is aged, after coating, for 67 hours at 5 C. The gel is then washed repeatedly with cold water until no trace of formaldehyde can be detected in the wash water (1-2 hours). The plate is dried and melting point studies made. Typical data are given in Table I.

The effect of varying pH and time and temperature of storage are shown by Tables 11 to IV.

After-hardening of coated plates can be reduced materially by washing the dried plate in water or a 1% urea solution followed by a water wash. Typical data are given in Tables VI to IX.

5 In the examples given in Tables I to V, the gel was washed and then dried, either before or after coating, after which it was aged. In the examples given in Tables VI to IX, the gel was coated, then dried prior to washing, after which it was aged.

' TABLE I Effect of ageing formaldehyde treated gelatin in the jelly state and of washing and drying on the TABLE II Effect of ageing of glycol aldehyde treated gelatin in the ielly state and of washing and drying on the after-hardening of the dried gelatin TABLE IV Eflect of ageing formaldehyde treated gelatin in the sol state, and of coating, washing and dry-' ing on the after-hardening of the dried gelatin 0.3 percent formaldehyde (on wt. of gelatin) p Aged 68 hrs. at 35 (95 F.) before washing 10 Age of dried gellatin,

Treated Treated Unmmd unwashed washed 33 (91.4" E.).... 75 (107 F). 45 (113 F 45 13 F 45 113 F g 45 113F.

33-34 (91.4-93. 2 F.) 97 (206 F.). 68 (154.4" F.)

TABLE V Effect of ageing formaldehyde treated gelatin in the sol state, and of coating, washing, remelting, coating and drying on the after-hardening of the dried gelatin 0.3% formaldehyde (on wt. of gelatin) p Aged 68 hrs. at C. (95 F.) before washing Age of dried ii T ted 'r ted tea tea Y8 Unmated unwashed washed 1.0 33 91.4 F. 75 167 F. 45 13 F. a 0 45 813 5 7 0 45 (113 F 12 0 45 (113 F 49.0 ear-34 (91.4-93.2" F.).. 9? (206 F.)-- 74 (165 2 F.)

TABLE VI 0.4% glycol aldehyde (on wt. of gelatin) 40 A d 9 h 25 H gl i b r m Effect of removal of nncombmed formaldehyde on ge 1 the after-hardening of formaldehyde treated .X-ray emulsion e Uncombined formaldehyde removed by washing dried emulsion M P" C 0.05% formaldehyde (on wt. of gelatin) 40 Age of dried gelatin, pH 6.6

5Y5 Treated Treated Untreated unwashed washed Age of M. P. C. a e o o I o 0 dried 33 914 F)- g7 202 F.) g emub I 0 e sion Treated Treated (131 11 Untreated ys unwashed washid 62.0 34 (932 F.). ---.-do--..-- 10 (158 F.)

1 0 s2-e4 see-932 F.). 3335(9195F.).. 35 05 F.) 6.0...... az-w see-932 11)-. 37 es.e F.) 35(95F.) 23.0.--" 32-34 se 0-932 39 102.2F.) 35 95" F.) 55 43.0-.- savanna-932 F. 40 104.0 F.)-. warn.) 55

TABLE III 1sa.0 ma mas-93.2%.)" 54 129.2 3e (963 F.)

Effect of ageing formaldehyde treated gelatin in the sol state, and of coating, washing, remelt- TABLE Vn ing, coating and drying on the after-hardening Effect of removal of uncombined formaldehyde on the after-hardening of formaldehyde treated 80 X -ray emulsion Uncombined formaldehyde removed by washing the dried emulsion 0.1% formaldehyde (011 wt. of gelatin) pH 6.6

M. P., "C

Treated Treated Untreated unwashed washed 3234 (ERG-93.2 F.) 36 (96.8 F 37 (98.6 3234 (89.6-93.2 F 49 (120 2" F.) 36 $96.8 3234 (89.15-93.2 F.) 79 (174 2 F). 38 A 32-34 589.6931 F.;. 81 (177 F.). 38 (100.4 F 32-34 89.693.2 F. 86 (186 8 F.). 39 (102 2 F TABLE VIII Effect of removal of uncombined formaldehyde on the after-hardening of formaldehyde treated X-ray emulsion l ncnmbined formaldehyde removed by washing the dried emulsion 0.18% formaldehyde (on wt. of gelatin) pH 6.6

Age of M. P. dried emu SlOD Treated un- Treated days Untreated washed waned .2" F.) 39 (102.2 F.) 38 100.4 F.) .2 F.) 66 (150.8 131;- 38 100.4 F.) 32 34 (89.693.2 F.) 76 (168.8 F. 37 (98.6 F.) 32-34 (89.6-93.2" F.)- 89 (l92.2 F.)- 39 (l02.2 F.)

TAnLn 1X E fiect of removal of uncombined formaldehyde on the after-hardening of formaldehyde-resorcinol treated X-ray emulsion odzhiormaldehyde our invention may also be used as a film overcoating or as a backing layer to reduce the curling tendency of cellulose ester film or to contain an anti-halation material. The pre-hardened gelatin may also be used as substrate between the film support and the emulsion layer or between the film support and other layers of the film.

It is to be understood that the examples reten-ed to above are by way of illustration only and that our invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. The method of preparing pre-hardened photographic gelatin which comprises treating un hardened gelatin with an aqueous solution of a hardening agent in an amount up to approxi mately 1 /270 of hardening agent based on the weight 01' gelatin until the desired hardening is obtained, and washing out the residual, uncombined hardening agent prior to coating the gela- 1.57 resor 01 (on wt. oi gelatin) Age of M. P., C.

dried emulgg Untreated Treated unwashed Treated washed 1.0 3234 (89.6-93.2 F.) M (HM-107.6 F.) 40-42 (l-107.6 .2 F. 44 111.2 37 nae F).

.2 F. 55 131.0 37 98.6 1 2 F 63 145.4" W 102. 1". 3 F. 62 143.6 1'. 40 10. F. 9811..-- 32-34" (89.593.2" F. 66 150.8" F.). 42 107. F. 182.0..." 32-34 (89.6'932" F.) 75 16.7 F.)-.. 47 116.6" F.

In the preparation of an emulsion according to our invention, the hardening process may be accelerated by heating in a moist atmosphere as described in our co-pending application of s. E. Sheppard, R. C. Houck, and R. H. Lambert, Serial No. 90,000 filed Ju1y 10, 1936. According to this method, a gelatino-silver halide emulsion is treated with the hardening agent prior to digestion, the excess hardening agent then washed out, and the emulsion coated on a suitable support and subjected to a heat treatment in a moist atmosphere at 60 to 70 C.

We have referred above to the melting point of the gelatin. The melting point of said gelatin varies with the water content and increases as the water content of the gel is reduced. The melting point of gels, as referred to above, is determined in the following way:

A strip of gelatin whose melting point is to be determined is coated on glass and immersed in distilled water and the temperature raised slowly (0.75 C. per minute). The temperature at which the gelatin flows rapidly .oi! the plate is taken as the melting point of the gelatin.

The pre-hardened gelatin made according to our invention may be used in a number of ways in the manufacture of photographic films or plates. When used to produce a hardened photographic emulsion, the pre -hardened gelatin is added to the emulsion preferably after the precipitation of the silver halide. The amount of pre-hardened gelatin added to the emulsion will depend of course upon the melting point oi the hardened gelatin and on the desired meltingpointof the final emulsion. Amounts may be used varying from .05% of the hardened gelatin to 1.0% compared with the amount 01 emulsion. The pre-hardened gelatin prepared according to tin on a photographic support.

2. The method of preparing pre-hardened photographic gelatin which comprises treating unhardened gelatin with an aqueous solution of formaldehyde in an amount up to approximately l of formaldehyde based on the weight of gelatin until the desired hardening is obtained, and washing out the residual, uncombined formaldehyde prior to coating the gelatin on a photographic support.

3. The method of preparing pre-hardened photographic gelatin which comprises treating unhardened gelatin with a hardening agent in an amount up to approximately 1 /2% 0! hardening agent based on the weight of gelatin until the gelatin attains a melting point of 40 C. to 70 C., and washing out the residual, uncombined hardening agent prior to coating the gelatin on a photographic support.

4. The method 01' preparing pre-hardened photographic gelatin which comprises treating unhardened gelatin with an aldehyde hardening agent in an amount up to approximately 1 /2% of hardening agent based on the weight of gelatin until the gelatin attains a melting point of 40 C. to 70 0., and washing out the residual, uncombined aldehyde hardening agent prior to coating the gelatin on a photographic support.

5. The method of preparing pre-hardened photographic gelatin which comprises treating unhardened gelatin with 9. formaldehyde in an amount up to approximately 136% of formaldehyde based on the weight of gelatin until the gelatin attains a melting point of 40 C. to 70 C., and washing out the residual, uncombined formaldehyde prior to coating the gelatin on a photographic support.

6. The method of preparing a photographic emulsion of substantially constant melting point, which comprises treating a gelatino-silver halide emulsion with an aldehyde hardening agent in an mount up to approximately 1%% of hardening agent based on the weight of gelatin, coating the emulsion on a support, drying the emulsion, and washing out the residual, uncombined hardening agent.

7. The method of preparing a photographic emulsion of substantially constant melting point, which comprises treating a gelatino-silver halide emulsion with an aldehyde hardening agent in an amount up to approximately 1Vz% of hardening agent based on the weight of gelatin, washing put the residual, uncombined hardening .agent, and drying the washed emulsion.

SAMUEL E. SHEPPARD. ROBERT C. HOUCK.

CERTIFICATE OF CORRECTION. Patent No. 2,227,982. r January 7, 19m.

SAMUEL E. SHEPPARD, El AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 15, Table IV, under the heading "Untreated" for "55 (91J+ E.)" read-"53" (91.h F'.)--'; and that the said Letters Patent should be read with this correction therein that the same may cenform to the-record of izhe case in the Patent Office.

Signed and. sealed this 18th day of March, A. D. 19m;

Henry Van Arsdale, (.Seal) Acting Commissioner-of Patents. 

